Follow the below path to edit the installment name

Method 1: System Admin Access Level

Settings --> Finance --> Create Fee Plan --> Select the Academic Year, Type of Fee Plan and click on Get --> Manage Fee Plans --> Click on View settings against the Fee Type --> Click on the installment name --> Update the installment name and click on Update to save the changes

Method 2: Branch Level Access

Finance --> Fee Management --> Manage Fee Plans --> Select the Academic Year, Type of Fee Plan and click on Get --> Manage Fee Plans --> Click on View settings against the Fee Type --> Click on the installment name --> Update the installment name and click on Update to save the changes